Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore

Spatial and Geometrical-Based Microstructure in Components Fabricated by Electron Beam Powder Bed Fusion

Pan Wang1,a, Mui Ling Sharon Nai1 and Yusaku Maruno2

1Singapore Institute of Manufacturing Technology, 73 Nanyang Drive, 637662, Singapore

2Materials Solution Centre, Hitachi Metals Singapore Pte. Ltd., Singapore 629656


Metal powder bed fusion additive manufacturing (PBF-AM) has attracted great attention from academics to industries in the recent decade. To accelerate the adoption of PBF-AM, its resultant microstructure at the printed component level must be fully understood so as to have tailorable microstructures that can cater to applications' needs. In this study, the microstructures of printed industrial components of different material systems (such as Ti-6Al-4V, Ti-48Al-2Cr-2Nb intermetallic and CM247LC) are investigated. The complex geometrical components with a wide variety of cross-sections that are fabricated by the electron beam (EB) PBF process achieve near fully dense and no distortion. It is found that the resultant microstructure is highly dependent on its material's type and the thermal histories experienced. For the case with Ti-6Al-4V, a gradual change in α+β microstructure and microhardness at different locations in the impeller is observed, which is attributed to the complex thermal gradient and its intrinsic heat treatment. For the case with Ti-48Al-2Cr-2Nb intermetallic, the observed microstructure changes slightly with different locations regarding the fraction and distribution of the coarse γ phase. The change in microstructure can be linked to the location of the sample and their thermal histories. High temperature caused a loss of Al content, in turn, an increase of α2 phase. For the case with CM247LC, the texture and grain size vary at different locations in the printed turbine wheel, which are attributed to the cooling speed and thermal gradient difference at different locations. These findings provide an in-depth understanding of the material-process-microstructure relationship in the EB-PBF. More importantly, the findings can be extended to a more broad alloys system, such as these alloys like Ti-6Al-4V, whose microstructures are sensitive to the heat input and heat accumulation during the EB-PBF process, these alloys with a high content of volatile elements (e.g. Mn, Mg, Al, Pb, Zn), such as in Ti-48Al-2Cr-2Nb alloys, resulted in elemental content difference at different locations as volatile elements evaporate more rapidly at hot locations, single-phase alloys (e.g. Co-Cr alloys, FCC high entropy alloys) or solid solution strengthening alloys (e.g. Inconel 625), where grain size strengthening and strain strengthening mechanisms dominate. Our findings shed the importance of spatial control of microstructure in the PBF AM processes.

Keywords: Thermal histories,Ti-6Al-4V, CM247LC, Ti-48Al-2Cr-2Nb intermetallic, Electron beam melting, Additive manufacturing.

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